The present invention relates to a liquid crystal display apparatus, and more particularly to a technology which is effective when applied to a liquid crystal display apparatus in which a display pixel of an active matrix-driven type and a driving circuit therefor are formed on a glass substrate or a silicon chip.
A liquid crystal panel is being widely used as a television set, a monitor of information devices such as a personal computer, and a display apparatus for the other various kinds of display apparatuses.
This kind of liquid crystal panel is constituted as follows: A driving electrode, which serves as an electrode of a switching element for selecting a pixel, is formed on one substrate, and a common electrode is formed on the other substrate. Then, sides of both the electrodes are opposed and laminated to each other with a gap, and a liquid crystal layer is disposed in the gap, to thereby constituting the panel.
In a structure in which an amorphous silicon thin film is employed for a channel layer of a FET switching element, there will be a limit to the characteristics as a transistor. If such structure is used to constitute a driving circuit, resulting characteristics will be insufficient, thus making it necessary to provide a peripheral driving circuit outside the glass substrate.
Meanwhile, the following type of display apparatus has been developed: A thin film transistor (hereinafter, referred to as TFT) is formed using a poly-silicon film, so that a driving circuit, as well as switching elements for selecting display pixels, is formed on one and the same glass substrate. Incidentally, concerning the TFT elements formed using the poly-silicon film, a product manufactured therefrom, about which the number of pixels is about one hundred thousand and diagonal length of a display area is 0.7 inches, is used as a color finder of a small-sized video camera.
Moreover, concerning the above-described TFT display apparatus in which the poly-silicon film is used, the utilization thereof has been developed as a display source of a projector or as a panel for a head mount (glasses-shaped) display designed for a virtual reality.
Furthermore, a polymer dispersion type liquid crystal (hereinafter, referred to as PDLC) display element has been developed in the following way: A common electrode is formed on a transparent substrate and a driving electrode is formed on a silicon substrate. Then, a liquid crystal layer of a macromolecule dispersion type is sandwiched in a lamination gap between both the electrodes, thus forming the PDLC.
In connection with the above-described methods of utilizing the TFT display apparatus in which the poly-silicon film is used or a display apparatus in which the PDLC is used, there is a liquid crystal projector optical system based on a three-color plates system. The three-plates system is a system employing a display apparatus which allows an image to be formed for each of colors of red, green and blue.
FIG. 1 shows a schematic diagram of the liquid crystal projector optical system based on the three-plates system. A light launched from a light source 850, which comprises, for example, a metal halide lamp and a parabolic surface mirror, reaches a dichroic mirror 851. Here, the dichroic mirror 851 has a function of allowing a light in a specific wavelength range to be reflected or to pass through. Thus, only a blue light is reflected with its direction changed by 90 degrees, and the other lights are permitted to pass through. The other lights which have passed through, i.e. transmitting lights, are launched into a dichroic mirror 852. Only a green light is reflected there, and a transmitting light turns out to be a red one. In this way, the lights resolved in the order of blue, green and red are each launched into specifically designed liquid crystal panels 853, 854 and 855. On each of the liquid crystal panels 853, 854 and 855, an image corresponding to each of the colors has been reproduced. Then, each of the incoming lights, after being modulated for each color, is superimposed.
At a dichroic mirror 856, the green light is reflected. The reflected green light is superimposed with the blue light which has passed through the liquid crystal panel 853. The superimposed light is further superimposed with the red light reflected by a dichroic mirror 857. The superimposed light is projected onto a screen by a projection lens.
In the optical system as described above, first, the blue transmitting light from the liquid crystal panel 853 has never been reflected even one time. Accordingly, the blue transmitting light is superimposed in such a state that the pattern on the liquid crystal panel remains unchanged, and then is launched into the projection lens. Then, the red transmitting light from the liquid crystal panel 855 undergoes a direction conversion by 90 degrees two times at a reflection mirror 858 and at the dichroic mirror 857. Consequently, as is the case with the blue transmitting light, the red transmitting light is superimposed in such a state that the pattern on the liquid crystal panel remains unchanged, and then is launched into the projection lens.
Moreover, the green transmitting light from the liquid crystal panel 854 undergoes a direction conversion by 90 degrees only one time at the dichroic mirror 856. Accordingly, the green transmitting light is launched into the projection lens with the pattern on the liquid crystal panel inverted from top to bottom or from right to left. On account of this, in order to make the images coincide with each other, it becomes necessary for the green liquid crystal panel 854 to display an image which is, in advance, inverted from top to bottom or from right to left. Incidentally, reference numeral 859 designates a reflection mirror.
In the green liquid crystal panel 854, in order to invert an image thereon from right to left or from top to bottom, the following methods are generally employed: An inversion driving circuit is newly provided, the green liquid crystal panel 854 is specially manufactured so that, in order to display the inverted image, it can scan in a direction opposite to that of the red and the blue liquid crystal panels 853, 855, image data is stored once in a memory and is then read out so that the image is inverted, and so on.
Namely, in the liquid crystal projector based on the three primary colors-separating system, only one color component of the color images differs in the number of times of inversion from the other color components. This situation causes the component through a usual liquid crystal panel to be inverted from right to left or from top to bottom, and thus it turns out that the usual liquid crystal panel outputs the inverted image. Accordingly, a specific structure is added to the usual liquid crystal panel so that it can output an inverted image independently. An example of such a liquid crystal panel as outputting the inverted image is indicated on pages 383-386 of SID 93 DIGEST (1993).